550 



PEOr. G. ELLIOT SMITH OX THE 



the resemblance of the pattern to that found in tlie Carnivora much moi'e obvious than 

 it is in other Lemurs, and, to a certain extent, justifies the comparison Avliich all 

 previous writers have instituted. 



It was, in fact, the search for an explanation for the extraordinarily puzzling arrange- 

 ment of the sulci in the brain of C/u'rowi/s-, which led me to conclude that the 

 sujirasylvian sulcus becomes merged in the " Sylvian fissure " in the Primates — an 

 hypothesis the accuracy of which has been so amply confirmed by later studies. 



In one brain, ^vhich I shall distinguish as u, a deep f uitow begins near the bend of the 

 rhinal fissure, and passes upward with a very slight backward inclination for a distance 

 of about 11 mm. This is the pseudosylvian sulcus (figs. 33 and 3i). 



Fig. 33. 



sec 



Fig- 34. si. 



SCO. 



S3. 



Fig. 33. — C/iiromt/s mud<tiia.iiar'iciis':s. Lateral aspeit of the left cerebral hemisphere. 

 Fig. 34. — Lateral aspect of the right cerebral hemisphere. 



An arched furrow formed by the union of the suprasylvian and postsylvian sulci, 

 after the manner of the pattern found in the Carniv^ora, surrounds the pseudosylvian 

 sulcus (figs. 32, 33, and 34). The suprasylvian sulcus begins at a distance of 5 mm. 

 in front of the upper part of the pseudosylvian, and arches obliquely upward and 

 backward to a point 15".j mm. from the mesial plane and 125 mm. in front of the 

 posterior margin of the hemisphere. At this jioint it joins the postsylvian sulcus, 

 and from the conjoint furrow a little ujiwardly-directed branch 2 mm. long is given 

 off. The postsylvian sulcus is 8'5 mm. behind the pseudosylvian sulcus. The two 

 hemispheres of the specimen a are practically symmetrical so far as these features are 

 concerned. 



In a second specimen (figs. 35 and 36), which I shall distinguish as /3, the suprasylvian 

 sulcus presents similar features to those just described in k ; but the postsylvian and 

 pseudosylvian have become so greatly distorted and broken up that a pattern is formed 

 which is quite unlike that exhibited by the specimen a. 



On the left hemispljere there is a much shorter and shallower pseudosylvian sulcus.' 

 The suprasylvian sulcus is separated from a very oblique sulcus (which is analogous to 

 the upper part of the postsylvian) by a narrow gyrus (fig. 35). And between this and 

 the small pseudosylvian there is a vertical sulcus (.r) \\hich is much longer and deeper 

 than either of the furrows between which it lies. It is clearly a furrow compensatory 

 to the fragmentary pseudosylvian and postsylvian sulci. Behind it there is a much 



